Various film forming apparatuses utilizing vapor deposition are used in manufacturing of semiconductor devices. In those film forming apparatuses, the pressure inside a film forming chamber, the partial pressures of material gases, etc. are accurately controlled to form thin films having thicknesses in units of nm. Accurately detecting those pressures is important in performing the accurate control. A capacitive pressure sensor is used for the purpose of such pressure detection (see Patent Literature (PTL) 1).
That type of pressure sensor includes, as illustrated in FIG. 3, a base 301 made of an insulator. The pressure sensor further includes a diaphragm 302 receiving pressure from a measurement target. The diaphragm 302 is made of an insulator and is supported over the base 301 by a support portion 301a. The diaphragm 302 is arranged in a movable region 302a in a spaced relation to the base 301. In addition, the diaphragm 302 is displaceable in the movable region 302a in a direction facing the base 301. The pressure sensor further includes an airtight chamber 303 formed between the diaphragm 302 in the movable region 302a and the base 301.
The pressure sensor further includes a movable electrode 304 formed in the movable region 302a of the diaphragm 302 inside the airtight chamber 303. The pressure sensor further includes a fixed electrode 305 formed on the base 301 inside the airtight chamber 303 in an opposing relation to the movable electrode 304. The pressure sensor further includes a movable reference electrode 306 formed in the movable region 302a of the diaphragm 302 around the movable electrode 304 inside the airtight chamber 303. The pressure sensor further includes a fixed reference electrode 307. The fixed reference electrode 307 is formed on the base 301 around the fixed electrode 305 inside the airtight chamber 303. The fixed reference electrode 307 is formed in an opposing relation to the movable reference electrode 306.
The pressure sensor having the above-described structure is mounted to a pipe through which a fluid as a measurement target flows or a tank in which a fluid to be measured is stored, thus measuring a pressure of the fluid. In the capacitive pressure sensor, a displacement of the movable region 302a of the diaphragm 302 having received the fluid pressure is converted to a capacitance value between the movable electrode 304 and the fixed electrode 305. That type of pressure sensor is widely used in industrial applications, including the above-mentioned equipment for use in manufacturing the semiconductor devices, because it is less dependent on the kinds of gas.